Y Arm End Station 1
The vacuum chambers inside LIGO Hanford's Y end station lie out of view to the left in this panorama, obscured by a temporary beam tube cap and other equipment. The panorama provides a nice view of a cryogenic pump (the large bulged portion of the beam tube) and a pair of gate valves, one on each side of the cryopump. Liquid nitrogen from a large outdoor storage tank circulates through the plumbing that's visible in the photo to chill the interior of the cryopump in order to freeze out stray water molecules in the vacuum. Monolayers of water molecules on LIGO's mirrors can absorb light from the infrared laser beam and disrupt the sensitivity of the detector.
The huge gate valves permit the partitioning of LIGO's vacuum system. A pair of gate valves brackets each of H1's eight cryopumps, but a number of additional gate valves, most of which reside in the main building's Laser and Vacuum Equipment Area (LVEA), allow for restricted venting of chamber volumes when work needs to occur inside the vacuum system. Venting the smallest possible volume in such cases reduces the risk associated with opening the vacuum, and speeds the pumpdown of the opened portion upon completion of the work.